2 Bulletin of the New York State Museum. 



many exceptions ; but in the greater number of these apparently 

 exceptional cases, the surface alteration, due to weathering or other 

 atmospheric agencies, explains the occurrence. 



This relation between the geological formation and the mineralogi- 

 cal species or kinds of iron ore, indicates the areas in which they may 

 occur, and determines roughly their limits. Hence, a geological map 

 of the State shows approximately correct boundaries of the several 

 iron-ore districts, and is, as it were, an iron-mines map. The geology 

 of a county or district, gives the clue in searching for ore ; and its 

 importance cannot be too strongly stated, both as a guide, suggesting 

 exploration, and warning against unnecessary and fruitless surveys 

 and wasteful outlays of time and money. Thus, for example, the 

 magnetites belong in the crystalline rock districts, and the search for 

 them in the later, sedimentary rocks of the adjacent territory would 

 be a hopeless task; or, again, the exploration of the Highlands or 

 Adirondacks, for carbonate ores, would be equally unscientific and 

 destitute of results. 



The geological formations, which are characterized as definite ore 

 horizons, become the basis of a natural arrangement of the ore dis- 

 tricts of the State. They are well marked geographically also, as 

 can be seen by reference to the map accompanying this report. This 

 map is on a scale of twenty miles to an inch, or y^sTFoo-) an( ^ snows 

 by its signs the location of the several mines, the kinds of ore, and 

 indirectly, the groups or iron-ore districts. 



Following this geologico-geographical arrangement, the groups 

 and iron-ore districts are : 



I. The Highlands of the Hudson. — Magnetic Iron Ores. 

 II. The Adirondack Eegion, Including the Lake Cham- 

 plain Mines. — Magnetic Iron Ores. 



III. The Hematites of Jefferson and St. Lawrence 



Counties. 



IV. The Clinton or Fossil Ores. 



V. The Limonites of Dutchess and Columbia Counties. 

 VI. The Limonites of Staten Island. 

 VII. The Carbonite Ores of the Hudson Eiver. 



A few isolated mines cannot be thus classified, as the hematite 

 near Canterbury, Orange county, Ackerman's mine near Unionville, 

 Westchester county, the Napanock and Wawarsing mines, in Ulster 

 county, the hematite of Mt. Defiance in Ticonderoga, and the bog 



